The present invention relates generally to an apparatus for neatly winding a film onto a reel or other structure and more particularly to an apparatus incorporating a flexible member for applying force to an edge of a film being wound such that the film pack is wound without scatterwinds and without damage to the film or the flexible member.
When a film is wound onto a reel, air is entrained between adjacent layers of film. The entrained air causes the adjacent layers of film to slip relative to each other before the air can bleed out and the film settles onto a film pack. The slipping between adjacent layers of film results in a displacement between the edges of the adjacent layers, subsequently, the edge of one layer may be higher or lower than the edge of an adjacent layer. A film pack being wound at high speeds can have many floating layers of film on the pack. Often, these floating layers become unstable and can shift large distances laterally. This is called scatterwinding. In extreme cases, without a flange present, the film can come completely off the reel. Scatterwinds create protruding edges of film that are subject to damage and cause the film to be misaligned when the film is unwound. The present invention minimizes scatterwinds without imposing excessive force on the film which could result in damage to the film or to the invention itself.
In minimizing scatterwinds it is desirable to minimize contact force and friction between the flexible member and the film being wound. Lower friction results in less wear to the film and the flexible member. Additionally, it is desirable to reduce or eliminate friction between the flexible member and the film when the film pack is being unwound.
There are many applications where a film, a tape, or other flexible material requires consistent and uniform collection onto a structure such as a spool, a hub, or a reel. Uniformity in winding of a film or the like onto a spool, for example, is necessary when the film is passed through a series of stationary guide elements that are aligned with the film path. Any misalignment of the film can result in excessive vibration, wear, and damage to the film as it passes through the guide elements.
Another advantage to eliminating scatterwinds in a film pack or the like, is in eliminating damage to the film caused by shipping, transportation, or handling of the film pack. A film pack having scatterwinds exposes displaced edges of the film to damage from the reel or similar structure that comes into contact with the exposed edges. A film having minimal scatterwinds is less susceptible to damage because the edges of adjacent film layers are aligned. The aligned edges form a substantially planar surface that spreads the contact force evenly across the surface of the film pack.
The present invention is applicable to reducing damage to a film that is repeatedly wound and unwound between two separate reels. By eliminating or reducing scatterwinds on the reel that is being wound, the film is subject to minimal wear and damage as it travels between the two reels. As a reel is being unwound to transfer the film to the other reel, reduced scatterwinds in the film pack of the reel being unwound provide for minimal lateral movement and vibration of the film as it travels to the reel that is being wound, thereby reducing additional wear or damage to the film as it interacts with other elements that come into contact with the film during the transfer.
Previous attempts at neatly packing a film onto a film pack include self-packing glass reels, liner sheets, magnetic force, and mechanical force.
Self-packing glass reels are precision tape reels with glass flanges. Spacing between the flanges is not less than the width of the tape at an inner diameter of the flange, however, the spacing between the flanges decreases slightly, in a radially outward direction, from the inner diameter to an outer diameter of the flange. The decreased spacing of the flanges constrains lateral motion of the tape, and as the tape pack enlarges, the tape pushes the flanges apart. The disadvantages of this solution are in the cost of the reels and the way in which the tape is rigidly guided by the flanges, making alignment with other guide elements in the tape path critical. Misalignment of the tape relative to the guide path can result in damage to the tape. Additionally, contact between the tape and the flanges results in tape edge damage and tape wear.
Liner sheets are typically used in cassette tape housings, for example DDS cassettes. In a DDS tape cassette, the tape reels have no flanges. Instead, there are two plastic liner sheets on either side of a tape pack. The liner sheets have stationary projections that extend outward of the liner sheet. The projections are in continuous contact with at least a portion of the tape pack. The liner sheets may be coated with a lubricant to reduce friction between the liner sheet and the tape pack. The projections in the liner sheet serve to urge the edges of the tape into alignment as the tape is wound onto the tape pack. There are several disadvantages to liner sheets. The projections contact the tape pack over a large area. As the tape is wound or unwound portions of the tape pack that come into contact with the projections are subject to friction and wear. As a result, after the projections have aligned the edges of the tape, the projections continue to make contact with the tape pack. In particular, heat caused by friction between the tape pack and the large contact area could become excessive at high tape winding speeds. The heating, friction, and wear associated with the liner sheets is exacerbated during the high winding speeds associated with fast forward and fast reverse tape winding.
Magnetic neat winding devices rely on magnetic fields generated by an electromagnet or a permanent magnet to align a film. The magnetic field urges the film into alignment by exerting magnetic forces on the film. The magnet may be positioned radially outward of the film pack or positioned above or below the film pack. Mechanical force from a pulley or the like may also be employed to aid in aligning the film. The main disadvantage of magnetic neat winding is that it requires that the medium being wound have magnetic properties. Additionally, the film must be blank to avoid erasure of magnetic data on the film. Further, the sophistication, power requirements, and size of the mechanisms required to implement magnetic neat winding preclude its use in portable applications.
Additionally, magnetic neat winding devices may incorporate pneumatics to assist in neat winding a film pack. A nozzle to evacuate air in the vicinity of the wound film is used to deplete air entrained between the film layers. Additionally, another nozzle can be used to blow air between film layers, thereby allowing adjacent film layers to float relative to each other. The floating layers allow for movement between the adjacent layers so that the film can be urged into position for alignment by the magnetic field. The disadvantage of using pneumatics to assist in magnetic neat winding is in the complexity, size, and cost of implementing a pneumatic system. Pneumatics are not amendable for use in portable film apparatus, can not be economically implemented in film cassettes or cartridges, and are mostly limited to neat winding of film in a production environment.
Mechanical neat winding devices generally use pulleys, capstans, pinch-rollers, guides, belts and the like to urge a film into alignment with a film pack or to constrain lateral movement of the film as it is being wound. Belts are used to either impinge on the surface of the film to displace air entrained between adjacent layers, or to contact an edge of the film as the film is being wound. To displace entrained air, the belt must apply a high pressure to the film, therefore, continuous contact between the belt and the film is required. The contact can result in embossing of the film by the belt. Belts are mechanically complex, bulky, and are not practical for portable neat winding applications. Pulleys, capstans, pinch-rollers, guides, and similar mechanical methods of neat winding a film pack use mechanical force to align a film. In a typical application these methods either displace entrained air by pressing against a film as it is wound or restrain lateral motion of the film as the film is wound. Restraining lateral movement of the film can also damage the film, particularly at the film edges. The main disadvantage of mechanical neat winding devices is the size and complexity required to accommodate a film pack of varying size.
From the foregoing it will be apparent that there is a need for a simple, portable, and economical means for reducing scatter winds in a film pack. Further, it will be apparent that low wear and minimal film damage are desirable properties in an apparatus for reducing scatterwinds.